Hey there, @derlehre!
Thanks for the context! What you are seeing is almost always down to the Persian (fa_IR) translation pack being incomplete or a little out of date rather than a broken setting. WooCommerce emails render in your site language, but only the strings that actually exist in the installed Persian translation get translated.
Anything the pack does not cover falls back to English, which is why you get that Persian and English mix. It also explains why it looked fully Persian a while back, since newer WooCommerce versions add new strings that the community translation may not have caught up on yet.
Here is what I would try, in order:
1. Double check that your Site Language is set to Persian under Settings > General, then save. This makes emails inherit the right locale. More on that here: https://woocommerce.com/document/woocommerce-localization/
2. Refresh your translations by going to Dashboard > Updates and clicking Update translations. This pulls the latest Persian pack and often closes the English gaps right away.
3. If some strings are still in English after that, it usually means those specific strings are not yet translated in the Persian project. You can see the current status (and even contribute the missing ones) here: https://translate.wordpress.org/projects/wp-plugins/woocommerce
4. Have a look at WooCommerce > Settings > Emails. If any subject, heading, or additional content fields were customized or saved in English, they will always show in English no matter the language pack. Leaving those fields empty lets WooCommerce use the translated defaults.
5. For any gaps that stick around, you can create your own upgrade safe translations with a tool like Loco Translate, stored in wp-content/languages/woocommerce/. The full guide covers this: https://woocommerce.com/document/woocommerce-localization/
One heads up from that guide: certain strings get stored in the database during the initial English install, so they can stay English until re-saved even after switching the language.
Give those a go and let me know how the emails look 🙂